If I purchase day saving ticket 2 nd class in advance and end up being able to get 1 at class reservation for one of the panoramic trains - will I be able to upgrade to 1 at class ticket and would I pay just the price difference between the 2 nd calls and 1 st class advance day saver ticket ? ( in this case the 2 nd class is 59 FR and the 1 st class is 88 F so the difference would be 29 FR. Please help me understand this process.